In certain applications, including transport refrigeration applications, it is common to drive a component, such as a refrigerant compressor, from one of two available prime movers, i.e., an internal combustion engine, such as a diesel engine, and a stand-by electric motor. When the electric motor is operative, the engine is commonly disconnected via a centrifugal clutch. Engine operating speeds are being reduced to reduce noise levels, and a centrifugal clutch is not suitable at some of the selected low operating speeds. Thus, the use of electromagnetic clutches instead of centrifugal clutches is becoming more attractive. Tests using electromagnetic clutches, however, especially when the electromagnetic clutch is operated in line between an engine flywheel and a refrigerant compressor, disclosed damage to the clutch plate return mechanism due to torsional oscillations inherent in the operation of small diesel engines. For example, compression springs which return the armature plate to a disengaged position following de-energization of the electromagnetic clutch, were damaged, as well as the spring bolts and the clearance holes for the spring bolts in an armature-flywheel adapter plate.
It would be desirable, and it is an object of the invention, to provide an electromagnetic clutch construction which reduces damage to the clutch plate return mechanism due to torsional oscillation in the driving force applied to the clutch from a driving source.